Methods and apparatus for determining flash point



1968 1... GROSS 3,408,856

METHODS AND APPARATUS FOR DETERMINING FLASH POINT Filed Sept. 14, 1964 2 Sheets-Sheet 1 (D L a INVENTOR LEWIS GROSS ATTORNEY L. GROSS 3,403,355

METHODS AND APPARATUS FOR DETERMINING FLASH POINT Nov. 5, 1968 2 Sheets-Sheet 2 Filed Sept. 14, 1964 DETECTOR, 40

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INVENTOR LEW/S GROSS FIGZ A TTORNEY United States Patent 6 3,408,856 METHODS AND APPARATUS FOR DETERMINING FLASH POINT Lewis Gross, 10646 Royal Springs Drive, Dallas, Tex. 75229 Continuation-impart of application Ser. No. 135,667,

Sept. 1, 1961. This application Sept. 14, 1964, Ser.

10 Claims. (Cl. 73--36) This invention relates to determining the flash point of materials. In particular, this invention is directed to methods and apparatus for continuously determining the flash point of flammable liquids.

This application is a continuation-in-part of patent application Ser. No. 135,667, filed Sept. 1, 1961, now abandoned.

In petroleum refineries and in the manufacture of solvents, the determination of the flash point of refined liquids is a critical quality control test. Such testing conventionally is accomplished by either a manual testing of samples in a laboratory or by instruments which take a sample of the liquid from the process and conduct a test on it in a manner analogous to a manual laboratory test.

It would be desirable if methods and apparatus were available for directly, simply, and continuously testing the flash point of materials as they are produced. It is readily seen that such methods and apparatus would make it possible to keep process variables set in accordance with flash point to continuously produce a product substantially all of which is within predetermined quality control limits for flash point.

The object of this invention is to provide methods and apparatus for continuously and automatically testing material, particularly a flammable liquid, for flash point, and to provide such methods and apparatus which are safe, simple, and reliable.

In connection with the object of safety, it is pointed out that the heating of flammable liquids in the presence of air is generally not considered to be an entirely satisfactory approach for testing since fire and/r explosion is apt to result through mishap.

In general, the various objects of this invention are accomplished by using a substitute method for that conventionally used in determination of the flash point of material. Flash point of flammable material is defined as that temperature at which vapors are being evolved rapidly enough to form a combustible mixture with air. According to this invention, the principle is used that for any material for which a flash point may be determined, there is a lower combustible limit of concentrations of its vapors in air. This lower combustible limit is sometimes referred to hereinafter as the lower explosive limit. For most hydrocarbon vapors, the lower explosive limit is at a concentration of approximately one percent by volume in air. Correspondingly according to Raoults law, this will be the temperature at which the material being tested has a vapor pressure corresponding to one percent of one atmosphere, or in other words, a vapor pressure of 7.6 mm. of mercury or 0.147 p.s.i.a.

This principle is applied in the present invention by maintaining the vapor pressure (or partial pressure if other materials are also present, as is in the case of one embodiment hereof) of a material being tested at a predetermined desired value which corresponds to the vapor pressure or partial pressure indicative of the lower explosive limits of the material (and hence the flash point of the material) were it in air. Such partial pressure or vapor pressure is maintained by adjusting temperature of the material being tested. The temperature of the material is measured and recorded. Such temperature is theflash point of the material, as determined by the methods and apparatus of this invention.

Viewed in one light, the present invention consists essentially of evolving vapors of a material to be tested at a rate comparable to the rate of evolution of vapors under conditions of exposure to air when the lower ex plosive limit therewith prevails. By controlling such rate of evolution of vapors and measuring the temperature of the material at whichsuch evolution occurs, the flash pointis determined The method of the present invention includes the principal steps of passing a quantity of a flammable fluid to be tested into a vessel, heating the fluid to evolve vapors, measuring the temperature of the fluid at which the vapors are evolved, measuring a property related to the vapors evolved from the fluid which is indicative of the rate of evolution of such vapors, and varying the heating of the fluid in the vessel in response to small variations in the measured property of the vapor to maintain the measured property of the fluid at an essentially constant value. The essentially constant value of the measured property is the value at which the rate of evolution of vapors from the fluid in the vessel is equivalent to the rate of evolution of vapors from the fluid under conditions of exposure to air which would correspond to the lower explosive limit of the vapors in air.

One preferred embodiment of the present invention comprises passing a stream of the combustible fluid to be tested through a vacuum and heating the fluid in the vacuum to a temperature at which vapors are evolved from the fluid removed at the vacuum pressure. The vacuum pressure is representative of that partial pressure equivalent to the lower explosive limit of the fluid and air. The temperature of the fluid is measured as it flows through the vacuum. This temperature measurement is taken under such conditions that substantially no change occurs in the vacuum pressure because of the rate of vapor evolution. The temperature measurement is the approximate equivalent of the flash point of the fluid and is the measured value by this method. In practice, heat is added or removed from the liquid as is required in order to maintain the rate of evolution of vapor such that the vacuum pressure is maintained at that value corresponding to the partial pressure of the liquid at its lower explosive limit with air. Fluid temperature is preferably measured continuously.

In another preferred embodiment, the vapor of the fluid to be tested is evolved into a carrier gas. The rate of evolution is maintained at an essentially constant value. This is accomplished by measuring a property related to the evolved vapor and changing the temperature of the fluid in accordance with small variations from a predetermined value of the property. The measured property is one which is indicative of the partial pressure of the fluid at the lower explosive limit, i.e. substantially at the flash point. In a preferred mode of practice of this embodiment, the thermal Lconductivity of the carrier gasvapor mixture is the measured property. The temperature of the fluid is changed to a different value by a suitable heating means in response to variations in the measured property from a predetermined value indicative of the rate of evolution of vapors which would correspond to the lower explosive limit of such vapors in air. Accordingly, the temperature of the fluid is maintained approximately at a value which is indicative of the flash point of the fluid that is being tested.

In the embodiment of this invention in which the evolution of vapors is conducted in a vacuum, the material being tested flows through a vacuum chamber which preferably is at a vacuum of approximately from 7 to 8 mm. of mercury. The temperature of the material in the chamber is raised or lowered by appropriate means in order to hold the liquid at a temperature at which the rate of release of vapors from the material does not cause a change in the vacuum pressure in the chamber and this temperature corresponds to a measurement of its approximate flash point. The chamber is evacuated by a positive displacement pump. A temperature sensitive device is used to measure the temperature of the material being tested at any instant and a pressure sensitive device c'om municateswith the chamber in order to respond to 'a change of the pressure within the chamber due to an in creasing or' lessening of the amount of vapors released from the material, and, accordingly, to regulate a heating means for either increasing or lessening the temperature of the materials so that the vacuum'in the chamber is brought back into the 7 to 8 mm. Hg'range.

For a more complete understanding of the present in vention and'for further objects and advantages 'thereo'f, reference may now be had to the following description taken in conjunction with the' accompanying drawings in which: i 1

FIGURE 1 is' a schematic view, partially in section, illustrating one preferred embodiment of an apparatus in accordance with the present invention; and

FIGURE 2 is a schematic view, partially in section, illustrating another preferred embodiment of an apparatus in accordance with the present invention.

Referring now to FIGURE 1 which illustrates apparatus which may be used to accomplish the vacuum type practice of the present invention, a flammable liquid flows through the main pipe line 2 shown therein. A portion of the liquid is drawn ofi through pipe 4, passed into insulated tank 6, and dropped on a heat conducting baflle 7 over which the liquid flows as a thin film 7a. The quantity being drawn off by pipe 4 is regulated by a suitable control device, in this example, by throttle valve 8. Liquid leaving baflle 7 is collected in the bottom of the tank and flows through pipe 10 into pump 12 by means of which it is pumped through pipe 14 back into pipe 2.

When the flammable fluid is a hydrocarbon mixture, a vacuum of from 7 to 8 mm. Hg, and preferably of 7.6 mm. Hg, is maintained in tank 6 by means of a vacuum line 15 joined to a positive displacement pump 16 which continuously removes vapors at a fixed rate from tank 6. These vapors are discharged from pump 16' through outlet line 18.

The quantity of vapor evolved from film 7a depends upon the temperature of the material forming the film 7a. An increase in the volume of vapors will be beyond the capacity of vacuum pump 16 and cause a rise in the pressure in tank 6. The reverse occurs when insufficient vapors are evolved from film 7a. To sense a change in the pressure within the tank 6, a pipe 20 communicates with a pressure sensitive device 22. This device in turn will vary the amount of current passing a control, such as variable resistor 24 mounted in the electrical supply line 26 and leading to an electrical heater 28 used for heating the baflle 7 and the film 7a, to raise or lower the heat of the film. Heater 28 is connected to the current source through return line 30.

Thermocouple 32, placed in the path of the liquid film 7a, is connected to a temperature indicating device 31 such as a thermometer. Conventional instruments are used for the pressure responsive device 22, the temperature indicating device 31, and the flow control device 8.

In this apparatus, the material to be tested for its flash point, for example, a flammable liquid such as kerosene, flows continuously over the heated baflle 7 in the form of a thin film which will evolve vapors at rates related to the temperature of the film. However, vacuum pump 16 strives to keep tank '6 at a vacuum of about 7.6 mm. Hg. If this pressure is exceeded by the vapors evolved from film 7a, pressure sensitive device 22 acts automatically to decrease the current supplied to heater 28 and thus to lower the temperature of film 7a to the point where the vapor pressure in tank 6 becomes steady at 7.6 mm. Hg.

The temperature of the film 711, as shown by the temperature indicating device 31, indicates the flash point of the material at that time. i

A change in the quality of the liquid flowing through pipe 2 (relating to flash point will quickly show up in the change in its flash point as isr'nea'sured by the temperature indicating device 31. J v

An example of .the operationofthe process in accordance with the vacuum aspect, as practiced by the ap paratus of FIGURE1-,-1S astollows:

Kerosene flowing throughpipe 2'-sho'uld have a vapor pressure of 7.6 mm. Hg at a temperature'of 135"F. A continuous strearn is' drawn oil arreugh pipe 4 and formed as a thin film 7a in tank 6, the incoming kerosene having a temperature of lOOYF. he tank 6 is evacuated by pump .16, and because insu'flicient vapors are evolved from the film 7a at a temperature of F., the vacuum in tank 6 drops below 7.6 mml'Hgand'the pressure sensi tive device 22 responds to energize heater 28 so that film 7a is heateduntil it evolves vapors and raises the temperature in tank 6 to 7.6 mm. Hg, When this occurs, the temperature indicating device 31'indicates a temperature of 132"R, which agrees quiteclosely'with the actual flash point of F. FIGURE 2 illustrates an alternative embodiment of the present invention. The apparatus illustrated therein makes it po'ssible'to evolve vapors"'from the flammable fluid to be tested into a carrier gas. Means are provided to sense the rate of vapor evolution, based on the concentration of the vapor in the carrier gas-vapor mixture, and maintain that evolution rate constant by varying temperature of the flammable fluid in accordance with any sensed changes from the desired control value of vapor evolution. As in the case previously illustrated in connection with FIGURE l, the rate of evolution which serves'as the predetermined rate to be maintained is based on the rate of evolution of vapor which would correspond to the lower explosive limit of the vapor in air, were the vapor being evolved from the fluid into air. This rate of evolution'is maintained such that a partial pressure of about 7 to 8 mm. Hg, preferably about 7.6 mm. Hg, of the flammable fluid prevails. Accordingly, of the total pressure of the fluid and carrier gas mixture, about 7,6 mm. Hg is attributable to the flammable fluid vapor and the balance of the total pressure to the carrier gas. Note that the system is preferably operated substantially at atmospheric pressure, which is one of its advantages over the apparatus described in connection with FIGURE 1 hereof. t I

' Referring now to FIGURE 2 in detail, a product flow line 51 for carrying flammable hydrocarbon liquid product from distillation equipment or the like has a small sample line 52, equipped with throttle valve 53, extending from it to a test vessel 54. The test vessel 54 carries a pair of thermal conductivity. cells 550 and 55b in a cylindrical container 55 extending through the upper head of the vessel 54. Such thermal conductivity cells are wellknown in the art and will, accordingly, not be described here. For a description, reference may be had to Gas Chromatography by Purnell (Wiley, 1962) and/ or to an article by Patton, Lewis .and Kaye, Analytical Chemistry, vol. 27, No. 2, pp. 474.

A gas supply source 56, for example, a cylinder 01 hydrogen, is connected to the upper portion of the vessel 54 by means of flow line 57. A flow control means 58, forexample a throttle valve, and a flow meter 59 are interposed in the line 57. The discharge of the line 57 is into the thermal conductivity cell 55a, which in turn communicates with the interior of vessel 54 through the long, downwardly extending tube 60, the discharge end of which lies below the level of liquid 61 maintained in the reduced lower diametrical portion of vessel 54. The lower portion of vessel 54 is provided with heating means, for example, by resistance heaters 62. A siphon 63 leads from the bottom of thevessel 54, with the intake end 64 disposed in the vessel to maintain the liquid therein at a desired lower level. The discharge end of siphon 63 leads to a sump or, alternatively, is connected by pump means to return fluid to the product flow line 51. Vapor outlet 65 extends from and communicates with the thermal conductivity cell 55b. Vapor outlet 65 leads to a stack, to a flare, or to other suitable exhaust disposal. The interior of the vessel 54 communicates with the thermal conductivity cell 55b through tube 66, which extends from the thermal sensed, is connected to a recording temperature controller 71 of conventional design. The recording temperature controller receives an input temperature from the sensing element 72, for example, a thermocouple disposed in the vessel 54 'to lie well below the liquid 61 therein. The output of the recording temperature controller 71 leads to a regulator means 73 in the power supply lines 75 for the resistance heaters 62. The regulator means may be, for example, a variable resistor to vary current through heating elements 62, or alternatively, a solenoid actuated switch to provide off and on action to the heating elements 62 in response to the output of the recording temperature controller 71.

In operation, a sample of the liquid product is continuously withdrawn from the product line 51 through the sample supply line 52, the desired rate of flow being maintained by the throttle valve 53 in line 52. The sample flows into the vessel 54 to join the quantity of fluid sample 61 in the bottom of the test vessel 54. It will be appreciated that since the quantity of sample fluid in vessel 54 is relatively small, a change in flash point of fresh sample entering throughline-52 will quite soon substantially aflect the flash point characteristics of the total accumulated sample in the vessel 54.

A carrier gas, for example, hydrogen, is conducted into the sample test vessel 54 through the thermal conductivity cell 55a and the discharge line 60, the bottom of which extends below the liquid level of the liquid 61 in the bottom of test vessel 54. The rate of carrier gas flow is set as desired by conventional throttle valve 58, or analogous means,'by reference to the flow meter 59. The level of liquid 61 in the test vessel 54 is maintained by the siphon 63. The carrier gas bubbles through the liquid 61, thus becoming saturated with the vapors from the liquid. The saturated gas then enters tube 66, passes through the thermal conductivity cell 55b, and finally discharges via the exhaust line 65.

The presence of the vapor from the flammable fluid in the saturated carrier gas causes an imbalance in the thermal conductivity sensed by each of the two channels of the detector 70, i.e. in the thermal conductivity of the carrier gas before and after saturation with vapor, as measured by thermal conductivity cells 55a and 55b, respectively. The detector 70 detects the deviation from a previously determined standard dilference in the two thermal conductivities. The previously determined standard corresponds to the lower explosion limit concentration of the vapors. When a deviation from the standard is detected, a signal is transmitted as the output from detector amplifier 70 to the recording temperature controller 71. The recording temperature controller 71 resets the heat input into the system by varying the electrical input to resistance heating elements 62. For example, a solenoid operated switch 73 is closed through the recording temperature controllers output to activate'the resistance heating elements 62 and thus transfer heat to the liquid 61 in the bottom of vessel 54 in response to a raising of the flash point characteristics of the liquid 61. Moreover, the recording temperature controller'records the sensed temperature input from the thermocouple 72 to provide 'a continuous record of the temperature of the liquid 61. This record is in fact a continuous record of the approximate flash point of the liquid product flowing in line 51.

Note that a change in the temperature of the fluid, as maintained by the regulator means 73, changes the vapor concentration in the carrier gas to correspond-with the new saturated gas characteristics for thevapor at the temperature at which the liquid is then maintained. Accordingly, the vapor concentration, and hence, rate of vapor evolution, iscontinuously maintained at the preset standard value, which corresponds to the vapor concentration, and hence, rate of evolution of vapor into the carrier gas, at the approximate flash point of the liquid being tested. It is thus seen that the apparatus of FIGURE 2 may be manipulated to continuously read and record the flash point of fluid product flowing in line 51.

The method of this invention is especially suitable for hydrocarbon stocks having medium or high flash points such as those of kerosene or higher. Hydrocarbon stocks having flash points of F. or higher do not need to be refrigerated to maintain them at the correct temperature while under a pressure of about 7.6 mm. Hg. In a petroleum refinery, the use of flash point controls is primarily for stocks having flash points of at least 95 F. While refrigeration is required in certain cases, a liquid heating and cooling system, including a steam heating and liquid coolant system, can be substituted for the electric heater 28. In all instances, the measurement of the flash point is continuous and does not require the assistance of laboratory aids in its operation.

The methods and apparatus of this invention are applicable to determination of flash point of flammable liquids generally, as well as of liquid hydrocarbons. For example, a 5% by weight solution of methanol in diethylene glycol has a flash point of 133 F., as determined by conventional methods. The lower explosive limit of methanol in air occurs at a partial pressure of the methanol vapor of 51 mm. Hg, which for the 5% solution of methanol in diethylene glycol is found to correspond to a temperature of about 127 F. Accordingly, the conventionally determined flash point and the flash point determined by the present invention (for example, by the apparatus of FIG- URE l and the methods described in connection therewith) vary by only 5 F. In the case of a 10% solution of methanol in diethylene glycol, the conventionally determined flash point is found to be F., while the flash point as determined by the present invention (i.e. based on a partial pressure of methanol of 51 mm. Hgthe explosive limit value) is 103 F. Thus, the conventionally determined flash point and that determined by the present invention are in quite good agreement.

In connection with the present invention, if desired, correction tables can be prepared so that any discrepancy between the temperature observed and the real flash point can be corrected. This is because of the close relation between the actual flash point and the boiling point temperature as, for example, a pure hydrocarbon at 8 mm. of Hg absolute pressure.

Thus using data such as above, the control for measured property (e.g. pressure and thermal conductivity in the specific embodiments described herein) can be adjusted so that more precise flash points of the material being tested are determined.

In order to establish the correct relationship between the flow quantity of the sample being tested and the capacity of the tank, lines and vacuum pump, the system may be calibrated with a material of known flash point determined by conventional laboratory methods.

A material having a flash point substantially below ambient temperature might be tested in a system providing a refrigeration unit for cooling but depending on heat transfer from ambient conditions for heating the cooled fluid. Since such a system and method does, in effect, provide means for heating (i.e. by transfer of heat from ambient), it is therefore intended that the term heating, as used in the claims hereof, cover such a system and method.

Having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.

What is claimed is:

1. A method for determining the flash point of a flammable fluid comprising the steps of passing a stream of said fluid through a vacuum, heating said fluid in the vacuum to a temperature at which vapors are evolved from the fluid and removed at the vacuum pressure maintaining said vacuum at a presure representative of that partial pressure equivalent to a lower explosive concentration of said fluid in air, and continuously measuring the temperature of the fluid as it flows through the vacuum at which no change occurs in the vacuum pressure because of the evolved vapors to give the approximate equivalent of the flash point of the fluid.

2. A method as in claim 1 wherein said fluid is a hydrocarbon mixture comprising the step of maintaining a vacuum at about 7.6mm. Hg.

3. An apparatus for the continuous measurement of the flash point of a fluid comprising a vacuum tank, vacuum pump means in communication with said tank, means for flowing the fluid through said tank, means for sensing the pressure in said tank, means for heating the tank responsive to said pressure sensing means for maintaining the fluid at a temperature at which vapors evolve from the fluid at the substantially constant vacuum pressure in said tank, and heat sensitive means for measuring said temperature to give the approximate flash point of the fluid.

4. A method for determining the flashpoint of a flammable fluid comprising:

(a) evolving vapors in an environment from a flammable fluid having a flashpoint subject to variation,

(b) passing a carrier gas through said environment to facilitate the evolution of said vapors,

(c) measuring a control property related to said evolved vapors that is indicative of the rate of evolution of said vapors,

(d) varying the rate of evolution of said vapors by transfer of heat in respect to said fluid in response to small variations in said measured control property to correct said rate of evolution to an essentially constant value which substantially equals the evolution of vapors from said fluid under conditions of exposure to air when the lower explosive limit of vapors from said fluid in air prevails, and

(e) measuring the temperature of said fluid to provide a direct indication of the approximate flashpoint of said fluid.

5. The method of claim 4 in which said control property is a function of the concentration of said vapors in said carrier gas.

6. The method of claim 4 in which said carrier gas is bubbled through said fluid to substantially saturate said carrier gas with said vapors, and in which measurement of said control property involves measuring the thermal conductivity of the subtantial1y saturated carrier gas.

7. The method of claim 4- in which said flammable fluid is withdrawn from a product line in a substantially continuous manner.

8. An apparatus for measuring the flash point of a flammable fluid comprising:

means for evolving vapors in said structure forming an oxygen-free environment, oxygen free environment from a flammable fluid having a flash point subject to variation, said means including means for heating said fluid;

means connected to said oxygen free environment to introduce a catrier gas to mix with said vapors from said fluid;

means for measuring a control property related to said evolved vapors without oxidizing said vapors that is indicative of the rate of evolution of said vapors;

means for varying the rate of evolution of said vapors, said last named means including control means to vary the heat output from said means for heating said fluid in response to small variations in said control property to the extent required to correct said control property to maintain it at an essentially constant value which is characteristic of a rate of evolution of vapors of said fluid in said oxygen free environment that is substantially equal to the rate of evolution of vapors from said fluid under conditions of exposure to air when the lower explosive limit of the vapors of said fluid in air prevails; and

means for measuring the temperature of said fluid.

9. The apparatus of claim 8 in which said means for measuring a control property includes means for measuring thermal conductivity of gaseous materials.

10. A method of determining the flashpoint of a flam mable fluid comprising:

(a) passing a quantity of said fluid into a vessel,

(b) evolving vapors from said fluid at a temperature below the normal boiling point of said fluid when under standard pressure,

(c) maintaining said vessel evacuated of substantially all gaseous materials except said vapors and maintaining the pressure in said vessel at substantially a subatmospheric value,

(d) continuously measuring the pressure of said vapors which is indicative of the rate of evolution of said vapors,

(e) transferring heat with respect to said fluid in said vessel in response to small variations in the measured pressure to correct for said small variations to substantially maintain said pressure of said fluid at an essentially constant value, said essentially constant value being that which is characteristic of a rate of evolution of vapors from said fluid in said vessel that is substantially equivalent to the evolution of vapors from said fluid under conditions of exposure to air when a lower explosive limit of the vapors of said fluid in air prevails, and

(f) measuring the temperature of said fluid in said vessel to provide a direct indication of the approximate flashpoint of said fluid.

References Cited UNITED STATES PATENTS 2,499,105 9/1945 Mercer 7317 FOREIGN PATENTS 124,359 6/ 1947 Australia.

OTHER REFERENCES A Study of the Relation Between Flash-point and Vapor Pressure of Burning Oil, 1923; 14, 15, 16, 17. Abstract of Dissertation, Ohio State University, E. G. Meiter.

RICHARD G. QUEISSER, Primary Examiner.

J. D. SCHNEIDER, Examiner.

C. I. MCCELLAND, Assistant Examiner.

PATENT OFFICE UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,408,856 November 5, 1968 Lewis Gross It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 40, after "tank," insert substantially constant flow Column 8, lines 6 and 7, cancel "structure forming an oxygen-free environment," and insert the same as an indented phrase between lines 5 and 6, same column 8.

Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A METHOD FOR DETERMINING THE FLASH POINT OF A FLAMMABLE FLUID COMPRISING THE STEPS OF PASSING A STREAM OF SAID FLUID THROUGH A VACUUM, HEATING SAID FLUID IN THE VACUUM TO A TEMPERATURE AT WHICH VAPORS ARE EVOLVED FROM THE FLUID AND REMOVED AT THE VACUUM PRESSURE MAINTAINING SAID VACUUM AT A PRESSURE REPRESENTATIVE OF THAT PARTIAL PRESSURE EQUIVALENT OT A LOWER EXPLOSIVE CONCENTRATION OF SAID FLUID IN AIR, AND CONTINUOUSLY MEASURING THE TEMPERATURE OF THE FLUID AS IT FLOWS THROUGH THE VACUUM AT WHICH NO CHANGE OCCURS IN THE VACUUM PRESSURE BECAUSE OF THE EVOLVED VAPORS TO GIVE THE APPROXIMATE EQUIVALENT OF THE FLASH POINT OF THE FLUID. 